Internet Engineering Task Force (IETF) M. Cotton
Request for Comments: 8126 PTI
BCP: 26 B. Leiba
Obsoletes: 5226 Huawei Technologies
Category: Best Current Practice T. Narten
ISSN: 2070-1721 IBM Corporation
June 2017
Guidelines for Writing an IANA Considerations Section in RFCs
Abstract
Many protocols make use of points of extensibility that use constants
to identify various protocol parameters. To ensure that the values
in these fields do not have conflicting uses and to promote
interoperability, their allocations are often coordinated by a
central record keeper. For IETF protocols, that role is filled by
the Internet Assigned Numbers Authority (IANA).
To make assignments in a given registry prudently, guidance
describing the conditions under which new values should be assigned,
as well as when and how modifications to existing values can be made,
is needed. This document defines a framework for the documentation
of these guidelines by specification authors, in order to assure that
the provided guidance for the IANA Considerations is clear and
addresses the various issues that are likely in the operation of a
registry.
This is the third edition of this document; it obsoletes RFC 5226.
Status of This Memo
This memo documents an Internet Best Current Practice.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
BCPs is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc8126.
Cotton, et al. Best Current Practice [Page 1]

RFC 8126 IANA Considerations Section in RFCs June 20171. Introduction
Many protocols make use of points of extensibility that use constants
to identify various protocol parameters. To ensure that the values
in these fields do not have conflicting uses and to promote
interoperability, their allocations are often coordinated by a
central record keeper. The Protocol field in the IP header [RFC791]
and MIME media types [RFC6838] are two examples of such
coordinations.
The IETF selects an IANA Functions Operator (IFO) for protocol
parameters defined by the IETF. In the contract between the IETF and
the current IFO (ICANN), that entity is referred to as the IANA
PROTOCOL PARAMETER SERVICES Operator, or IPPSO. For consistency with
past practice, the IFO or IPPSO is referred to in this document as
"IANA" [RFC2860].
In this document, we call the range of possible values for such a
field a "namespace". The binding or association of a specific value
with a particular purpose within a namespace is called an assignment
(or, variously: an assigned number, assigned value, code point,
protocol constant, or protocol parameter). The act of assignment is
called a registration, and it takes place in the context of a
registry. The terms "assignment" and "registration" are used
interchangeably throughout this document.
To make assignments in a given namespace prudently, guidance
describing the conditions under which new values should be assigned,
as well as when and how modifications to existing values can be made,
is needed. This document defines a framework for the documentation
of these guidelines by specification authors, in order to assure that
the guidance for the IANA Considerations is clear and addresses the
various issues that are likely in the operation of a registry.
Typically, this information is recorded in a dedicated section of the
specification with the title "IANA Considerations".
1.1. Keep IANA Considerations for IANA
The purpose of having a dedicated IANA Considerations section is to
provide a single place to collect clear and concise information and
instructions for IANA. Technical documentation should reside in
other parts of the document; the IANA Considerations should refer to
these other sections by reference only (as needed). Using the IANA
Considerations section as primary technical documentation both hides
it from the target audience of the document and interferes with
IANA's review of the actions they need to take.
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RFC 8126 IANA Considerations Section in RFCs June 2017
An ideal IANA Considerations section clearly enumerates and specifies
each requested IANA action; includes all information IANA needs, such
as the full names of all applicable registries; and includes clear
references to elsewhere in the document for other information.
The IANA actions are normally phrased as requests for IANA (such as,
"IANA is asked to assign the value TBD1 from the Frobozz
Registry..."); the RFC Editor will change those sentences to reflect
the actions taken ("IANA has assigned the value 83 from the Frobozz
Registry...").
1.2. For Updated Information
IANA maintains a web page that includes additional clarification
information beyond what is provided here, such as minor updates and
summary guidance. Document authors should check that page. Any
significant updates to the best current practice will have to feed
into updates to BCP 26 (this document), which is definitive.
<https://iana.org/help/protocol-registration>
1.3. A Quick Checklist Upfront
It's useful to be familiar with this document as a whole. But when
you return for quick reference, here are checklists for the most
common things you'll need to do and references to help with the less
common ones.
In general...
1. Put all the information that IANA will need to know into the
"IANA Considerations" section of your document (see Section 1.1).
2. Try to keep that section only for information to IANA and to
designated expert reviewers; put significant technical
information in the appropriate technical sections of the document
(see Section 1.1).
3. Note that the IESG has the authority to resolve issues with IANA
registrations. If you have any questions or problems, you should
consult your document shepherd and/or working group chair, who
may ultimately involve an Area Director (see Section 3.3).
Cotton, et al. Best Current Practice [Page 5]

RFC 8126 IANA Considerations Section in RFCs June 2017
If you are creating a new registry...
1. Give the registry a descriptive name and provide a brief
description of its use (see Section 2.2).
2. Identify any registry grouping that it should be part of (see
Section 2.1).
3. Clearly specify what information is required in order to register
new items (see Section 2.2). Be sure to specify data types,
lengths, and valid ranges for fields.
4. Specify the initial set of items for the registry, if applicable
(see Section 2.2).
5. Make sure the change control policy for the registry is clear to
IANA, in case changes to the format or policies need to be made
later (see Sections 2.3 and 9.5).
6. Select a registration policy -- or a set of policies -- to use
for future registrations (see Section 4, and especially note
Sections 4.11 and 4.12).
7. If you're using a policy that requires a designated expert
(Expert Review or Specification Required), understand Section 5
and provide review guidance to the designated expert (see
Section 5.3).
8. If any items or ranges in your registry need to be reserved for
special use or are otherwise unavailable for assignment, see
Section 6.
If you are registering into an existing registry...
1. Clearly identify the registry by its exact name and optionally by
its URL (see Section 3.1).
2. If the registry has multiple ranges from which assignments can be
made, make it clear which range is requested (see Section 3.1).
3. Avoid using specific values for numeric or bit assignments, and
let IANA pick a suitable value at registration time (see
Section 3.1). This will avoid registration conflicts among
multiple documents.
Cotton, et al. Best Current Practice [Page 6]

RFC 8126 IANA Considerations Section in RFCs June 2017
4. For "reference" fields, use the document that provides the best
and most current documentation for the item being registered.
Include section numbers to make it easier for readers to locate
the relevant documentation (see Sections 3.1 and 7).
5. Look up (in the registry's reference document) what information
is required for the registry and accurately provide all the
necessary information (see Section 3.1).
6. Look up (in the registry's reference document) any special rules
or processes there may be for the registry, such as posting to a
particular mailing list for comment, and be sure to follow the
process (see Section 3.1).
7. If the registration policy for the registry does not already
dictate the change control policy, make sure it's clear to IANA
what the change control policy is for the item, in case changes
to the registration need to be made later (see Section 9.5).
If you're writing a "bis" document or otherwise making older
documents obsolete, see Section 8.
If you need to make an early registration, such as for supporting
test implementations during document development, rather than waiting
for your document to be finished and approved, see [RFC7120].
If you need to change the format/contents or policies for an existing
registry, see Section 2.4.
If you need to update an existing registration, see Section 3.2.
If you need to close down a registry because it is no longer needed,
see Section 9.6.
2. Creating and Revising Registries
Defining a registry involves describing the namespaces to be created,
listing an initial set of assignments (if applicable), and
documenting guidelines on how future assignments are to be made.
When defining a registry, consider structuring the namespace in such
a way that only top-level assignments need to be made with central
coordination, and those assignments can delegate lower-level
assignments so coordination for them can be distributed. This
lessens the burden on IANA for dealing with assignments, and is
particularly useful in situations where distributed coordinators have
better knowledge of their portion of the namespace and are better
suited to handling those assignments.
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RFC 8126 IANA Considerations Section in RFCs June 20172.1. Organization of Registries
All registries are anchored from the IANA "Protocol Registries" page:
<https://www.iana.org/protocols>
That page lists registries in protocol category groups, placing
related registries together and making it easier for users of the
registries to find the necessary information. Clicking on the title
of one of the registries on the IANA Protocol Registries page will
take the reader to the details page for that registry.
Unfortunately, we have been inconsistent in how we refer to these
entities. The group names, as they are referred to here, have been
variously called "protocol category groups", "groups", "top-level
registries", or just "registries". The registries under them have
been called "registries" or "sub-registries".
Regardless of the terminology used, document authors should pay
attention to the registry groupings, should request that related
registries be grouped together to make related registries easier to
find, and, when creating a new registry, should check whether that
registry might best be included in an existing group. That grouping
information should be clearly communicated to IANA in the registry
creation request.
2.2. Documentation Requirements for Registries
Documents that create a new namespace (or modify the definition of an
existing space) and that expect IANA to play a role in maintaining
that space (serving as a repository for registered values) must
provide clear instructions on details of the namespace, either in the
IANA Considerations section or referenced from it.
In particular, such instructions must include:
The name of the registry
This name will appear on the IANA web page and will be referred to
in future documents that need to allocate a value from the new
space. The full name (and abbreviation, if appropriate) should be
provided. It is highly desirable that the chosen name not be
easily confused with the name of another registry.
When creating a registry, the group that it is a part of must be
identified using its full name, exactly as it appears in the
Protocol Registries list.
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RFC 8126 IANA Considerations Section in RFCs June 2017
Providing a URL to precisely identify the registry helps IANA
understand the request. Such URLs can be removed from the RFC
prior to final publication or left in the document for reference.
If you include iana.org URLs, IANA will provide corrections, if
necessary, during their review.
Required information for registrations
This tells registrants what information they have to include in
their registration requests. Some registries require only the
requested value and a reference to a document where use of the
value is defined. Other registries require a more detailed
registration template that describes relevant security
considerations, internationalization considerations, and other
such information.
Applicable registration policy
The policy that will apply to all future requests for
registration. See Section 4.
Size, format, and syntax of registry entries
What fields to record in the registry, any technical requirements
on registry entries (valid ranges for integers, length limitations
on strings, and such), and the exact format in which registry
values should be displayed. For numeric assignments, one should
specify whether values are to be recorded in decimal, in
hexadecimal, or in some other format.
Strings are expected to be ASCII, and it should be clearly
specified whether case matters, and whether, for example, strings
should be shown in the registry in uppercase or lowercase.
Strings that represent protocol parameters will rarely, if ever,
need to contain non-ASCII characters. If non-ASCII characters are
really necessary, instructions should make it very clear that they
are allowed and that the non-ASCII characters should be
represented as Unicode characters using the "(U+XXXX)" convention.
Anyone creating such a registry should think carefully about this
and consider internationalization advice such as that in
[RFC7564], Section 10.
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RFC 8126 IANA Considerations Section in RFCs June 2017
Initial assignments and reservations
Any initial assignments or registrations to be included. In
addition, any ranges that are to be reserved for "Private Use",
"Reserved", "Unassigned", etc. (see Section 6) should be
indicated.
For example, a document might specify a new registry by including:
---------------------------------------------------------------
X. IANA Considerations
This document defines a new DHCP option, entitled "FooBar" (see
Section y), and assigns a value of TBD1 from the DHCP Option space
<https://www.iana.org/assignments/bootp-dhcp-parameters>
[RFC2132] [RFC2939]:
Data
Tag Name Length Meaning
---- ---- ------ -------
TBD1 FooBar N FooBar server
The FooBar option also defines an 8-bit FooType field, for which
IANA is to create and maintain a new registry entitled
"FooType values" used by the FooBar option. Initial values for the
DHCP FooBar FooType registry are given below; future assignments
are to be made through Expert Review [BCP26]. Assignments consist
of a DHCP FooBar FooType name and its associated value.
Value DHCP FooBar FooType Name Definition
---- ------------------------ ----------
0 Reserved
1 Frobnitz RFCXXXX, Section y.1
2 NitzFrob RFCXXXX, Section y.2
3-254 Unassigned
255 Reserved
---------------------------------------------------------------
For examples of documents that establish registries, consult
[RFC3575], [RFC3968], and [RFC4520].
Any time IANA includes names and contact information in the public
registry, some individuals might prefer that their contact
information not be made public. In such cases, arrangements can be
made with IANA to keep the contact information private.
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RFC 8126 IANA Considerations Section in RFCs June 20172.3. Specifying Change Control for a Registry
Registry definitions and registrations within registries often need
to be changed after they are created. The process of making such
changes is complicated when it is unclear who is authorized to make
the changes. For registries created by RFCs in the IETF stream,
change control for the registry lies by default with the IETF, via
the IESG. The same is true for value registrations made in IETF-
stream RFCs.
Because registries can be created and registrations can be made
outside the IETF stream, it can sometimes be desirable to have change
control outside the IETF and IESG, and clear specification of change
control policies is always helpful.
It is advised, therefore, that all registries that are created
clearly specify a change control policy and a change controller. It
is also advised that registries that allow registrations from outside
the IETF stream include, for each value, the designation of a change
controller for that value. If the definition or reference for a
registered value ever needs to change, or if a registered value needs
to be deprecated, it is critical that IANA know who is authorized to
make the change. For example, the Media Types registry [RFC6838]
includes a "Change Controller" in its registration template. See
also Section 9.5.
2.4. Revising Existing Registries
Updating the registration process or making changes to the format of
an already existing (previously created) registry (whether created
explicitly or implicitly) follows a process similar to that used when
creating a new registry. That is, a document is produced that makes
reference to the existing namespace and then provides detailed
guidance for handling assignments in the registry or detailed
instructions about the changes required.
If a change requires a new column in the registry, the instructions
need to be clear about how to populate that column for the existing
entries. Other changes may require similar clarity.
Such documents are normally processed with the same document status
as the document that created the registry. Under some circumstances,
such as with a straightforward change that is clearly needed (such as
adding a "status" column), or when an earlier error needs to be
corrected, the IESG may approve an update to a registry without
requiring a new document.
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RFC 8126 IANA Considerations Section in RFCs June 2017
Example documents that updated the guidelines for assignments in
pre-existing registries include: [RFC6895], [RFC3228], and [RFC3575].
3. Registering New Values in an Existing Registry3.1. Documentation Requirements for Registrations
Often, documents request an assignment in an existing registry (one
created by a previously published document).
Such documents should clearly identify the registry into which each
value is to be registered. Use the exact registry name as listed on
the IANA web page, and cite the RFC where the registry is defined.
When referring to an existing registry, providing a URL to precisely
identify the registry is helpful (see Section 2.2).
There is no need to mention what the assignment policy is when making
new assignments in existing registries, as that should be clear from
the references. However, if multiple assignment policies might
apply, as in registries with different ranges that have different
policies, it is important to make it clear which range is being
requested, so that IANA will know which policy applies and can assign
a value in the correct range.
Be sure to provide all the information required for a registration,
and follow any special processes that are set out for the registry.
Registries sometimes require the completion of a registration
template for registration or ask registrants to post their request to
a particular mailing list for discussion prior to registration. Look
up the registry's reference document: the required information and
special processes should be documented there.
Normally, numeric values to be used are chosen by IANA when the
document is approved; drafts should not specify final values.
Instead, placeholders such as "TBD1" and "TBD2" should be used
consistently throughout the document, giving each item to be
registered a different placeholder. The IANA Considerations should
ask the RFC Editor to replace the placeholder names with the IANA-
assigned values. When drafts need to specify numeric values for
testing or early implementations, they will either request early
allocation (see Section 3.4) or use values that have already been set
aside for testing or experimentation (if the registry in question
allows that without explicit assignment). It is important that
drafts not choose their own values, lest IANA assign one of those
values to another document in the meantime. A draft can request a
specific value in the IANA Considerations section, and IANA will
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RFC 8126 IANA Considerations Section in RFCs June 2017
accommodate such requests when possible, but the proposed number
might have been assigned to some other use by the time the draft is
approved.
Normally, text-string values to be used are specified in the
document, as collisions are less likely with text strings. IANA will
consult with the authors if there is, in fact, a collision, and a
different value has to be used. When drafts need to specify string
values for testing or early implementations, they sometimes use the
expected final value. But it is often useful to use a draft value
instead, possibly including the draft version number. This allows
the early implementations to be distinguished from those implementing
the final version. A document that intends to use "foobar" in the
final version might use "foobar-testing-draft-05" for the -05 version
of the draft, for example.
For some registries, there is a long-standing policy prohibiting
assignment of names or codes on a vanity or organization-name basis.
For example, codes might always be assigned sequentially unless there
is a strong reason for making an exception. Nothing in this document
is intended to change those policies or prevent their future
application.
As an example, the following text could be used to request assignment
of a DHCPv6 option number:
IANA is asked to assign an option code value of TBD1 to the DNS
Recursive Name Server option and an option code value of TBD2 to
the Domain Search List option from the DHCP option code space
defined in Section 24.3 of RFC 3315.
The IANA Considerations section should summarize all of the IANA
actions, with pointers to the relevant sections elsewhere in the
document as appropriate. Including section numbers is especially
useful when the reference document is large; the section numbers will
make it easier for those searching the reference document to find the
relevant information.
When multiple values are requested, it is generally helpful to
include a summary table of the additions/changes. It is also helpful
for this table to be in the same format as it appears or will appear
on the IANA web site. For example:
Value Description Reference
-------- ------------------- ---------
TBD1 Foobar this RFC, Section 3.2
TBD2 Gumbo this RFC, Section 3.3
TBD3 Banana this RFC, Section 3.4Cotton, et al. Best Current Practice [Page 13]

RFC 8126 IANA Considerations Section in RFCs June 2017
Note: In cases where authors feel that including the full table of
changes is too verbose or repetitive, authors should still include
the table in the draft, but may include a note asking that the table
be removed prior to publication of the final RFC.
3.2. Updating Existing Registrations
Even after a number has been assigned, some types of registrations
contain additional information that may need to be updated over time.
For example, MIME media types, character sets, and language tags
typically include more information than just the registered value
itself, and may need updates to items such as point-of-contact
information, security issues, pointers to updates, and literature
references.
In such cases, the document defining the namespace must clearly state
who is responsible for maintaining and updating a registration.
Depending on the registry, it may be appropriate to specify one or
more of:
o Letting registrants and/or nominated change controllers update
their own registrations, subject to the same constraints and
review as with new registrations.
o Allowing attachment of comments to the registration. This can be
useful in cases where others have significant objections to a
registration, but the author does not agree to change the
registration.
o Designating the IESG, a designated expert, or another entity as
having the right to change the registrant associated with a
registration and any requirements or conditions on doing so. This
is mainly to get around the problem when a registrant cannot be
reached in order to make necessary updates.
3.3. Overriding Registration Procedures
Experience has shown that the documented IANA considerations for
individual protocols do not always adequately cover the reality of
registry operation or are not sufficiently clear. In addition,
documented IANA considerations are sometimes found to be too
stringent to allow even working group documents (for which there is
strong consensus) to perform a registration in advance of actual RFC
publication.
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RFC 8126 IANA Considerations Section in RFCs June 2017
In order to allow assignments in such cases, the IESG is granted
authority to override registration procedures and approve assignments
on a case-by-case basis.
The intention here is not to overrule properly documented procedures
or to obviate the need for protocols to properly document their IANA
considerations. Rather, it is to permit assignments in specific
cases where it is obvious that the assignment should just be made,
but updating the IANA process beforehand is too onerous.
When the IESG is required to take action as described above, it is a
strong indicator that the applicable registration procedures should
be updated, possibly in parallel with the work that instigated it.
IANA always has the discretion to ask the IESG for advice or
intervention when they feel it is needed, such as in cases where
policies or procedures are unclear to them, where they encounter
issues or questions they are unable to resolve, or where registration
requests or patterns of requests appear to be unusual or abusive.
3.4. Early Allocations
IANA normally takes its actions when a document is approved for
publication. There are times, though, when early allocation of a
value is important for the development of a technology, for example,
when early implementations are created while the document is still
under development.
IANA has a mechanism for handling such early allocations in some
cases. See [RFC7120] for details. It is usually not necessary to
explicitly mark a registry as allowing early allocation, because the
general rules will apply.
4. Choosing a Registration Policy and Well-Known Policies
A registration policy is the policy that controls how new assignments
in a registry are accepted. There are several issues to consider
when defining the registration policy.
If the registry's namespace is limited, assignments will need to be
made carefully to prevent exhaustion.
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RFC 8126 IANA Considerations Section in RFCs June 2017
Even when the space is essentially unlimited, it is still often
desirable to have at least a minimal review prior to assignment in
order to:
o prevent the hoarding of or unnecessary wasting of values. For
example, if the space consists of text strings, it may be
desirable to prevent entities from obtaining large sets of strings
that correspond to desirable names (existing company names, for
example).
o provide a sanity check that the request actually makes sense and
is necessary. Experience has shown that some level of minimal
review from a subject matter expert is useful to prevent
assignments in cases where the request is malformed or not
actually needed (for example, an existing assignment for an
essentially equivalent service already exists).
Perhaps most importantly, unreviewed extensions can impact
interoperability and security. See [RFC6709].
When the namespace is essentially unlimited and there are no
potential interoperability or security issues, assigned numbers can
usually be given out to anyone without any subjective review. In
such cases, IANA can make assignments directly, provided that IANA is
given detailed instructions on what types of requests it should
grant, and it is able to do so without exercising subjective
judgment.
When this is not the case, some level of review is required.
However, it's important to balance adequate review and ease of
registration. In many cases, those making registrations will not be
IETF participants; requests often come from other standards
organizations, from organizations not directly involved in standards,
from ad-hoc community work (from an open-source project, for
example), and so on. Registration must not be unnecessarily
difficult, unnecessarily costly (in terms of time and other
resources), nor unnecessarily subject to denial.
While it is sometimes necessary to restrict what gets registered
(e.g., for limited resources such as bits in a byte, or for items for
which unsupported values can be damaging to protocol operation), in
many cases having what's in use represented in the registry is more
important. Overly strict review criteria and excessive cost (in time
and effort) discourage people from even attempting to make a
registration. If a registry fails to reflect the protocol elements
actually in use, it can adversely affect deployment of protocols on
the Internet, and the registry itself is devalued.
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RFC 8126 IANA Considerations Section in RFCs June 2017
Therefore, it is important to think specifically about the
registration policy, and not just pick one arbitrarily nor copy text
from another document. Working groups and other document developers
should use care in selecting appropriate registration policies when
their documents create registries. They should select the least
strict policy that suits a registry's needs, and look for specific
justification for policies that require significant community
involvement (those stricter than Expert Review or Specification
Required, in terms of the well-known policies). The needs here will
vary from registry to registry, and, indeed, over time, and this BCP
will not be the last word on the subject.
The following policies are defined for common usage. These cover a
range of typical policies that have been used to describe the
procedures for assigning new values in a namespace. It is not
strictly required that documents use these terms; the actual
requirement is that the instructions to IANA be clear and
unambiguous. However, use of these terms is strongly recommended
because their meanings are widely understood. Newly minted policies,
including ones that combine the elements of procedures associated
with these terms in novel ways, may be used if none of these policies
are suitable; it will help the review process if an explanation is
included as to why that is the case. The terms are fully explained
in the following subsections.
1. Private Use
2. Experimental Use
3. Hierarchical Allocation
4. First Come First Served
5. Expert Review
6. Specification Required
7. RFC Required
8. IETF Review
9. Standards Action
10. IESG Approval
It should be noted that it often makes sense to partition a namespace
into multiple categories, with assignments within each category
handled differently. Many protocols now partition namespaces into
two or more parts, with one range reserved for Private or
Experimental Use while other ranges are reserved for globally unique
assignments assigned following some review process. Dividing a
namespace into ranges makes it possible to have different policies in
place for different ranges and different use cases.
Similarly, it will often be useful to specify multiple policies in
parallel, with each policy being used under different circumstances.
For more discussion of that topic, see Section 4.12.
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RFC 8126 IANA Considerations Section in RFCs June 2017
Examples of RFCs that specify multiple policies in parallel:
LDAP [RFC4520]
TLS ClientCertificateType Identifiers [RFC5246] (as detailed in
the subsections below)
MPLS Pseudowire Types Registry [RFC4446]
4.1. Private Use
Private Use is for private or local use only, with the type and
purpose defined by the local site. No attempt is made to prevent
multiple sites from using the same value in different (and
incompatible) ways. IANA does not record assignments from registries
or ranges with this policy (and therefore there is no need for IANA
to review them) and assignments are not generally useful for broad
interoperability. It is the responsibility of the sites making use
of the Private Use range to ensure that no conflicts occur (within
the intended scope of use).
Examples:
Site-specific options in DHCP [RFC2939]
Fibre Channel Port Type Registry [RFC4044]
TLS ClientCertificateType Identifiers 224-255 [RFC5246]
4.2. Experimental Use
Experimental Use is similar to Private Use, but with the purpose
being to facilitate experimentation. See [RFC3692] for details.
IANA does not record assignments from registries or ranges with this
policy (and therefore there is no need for IANA to review them) and
assignments are not generally useful for broad interoperability.
Unless the registry explicitly allows it, it is not appropriate for
documents to select explicit values from registries or ranges with
this policy. Specific experiments will select a value to use during
the experiment.
When code points are set aside for Experimental Use, it's important
to make clear any expected restrictions on experimental scope. For
example, say whether it's acceptable to run experiments using those
code points over the open Internet or whether such experiments should
be confined to more closed environments. See [RFC6994] for an
example of such considerations.
Example:
Experimental Values in IPv4, IPv6, ICMPv4, ICMPv6, UDP, and TCP
Headers [RFC4727]
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With Hierarchical Allocation, delegated administrators are given
control over part of the namespace and can assign values in that part
of the namespace. IANA makes allocations in the higher levels of the
namespace according to one of the other policies.
Examples:
o DNS names - IANA manages the top-level domains (TLDs), and, as
[RFC1591] says:
Under each TLD may be created a hierarchy of names. Generally,
under the generic TLDs the structure is very flat. That is,
many organizations are registered directly under the TLD, and
any further structure is up to the individual organizations.
o Object Identifiers - defined by ITU-T recommendation X.208.
According to <http://www.alvestrand.no/objectid/>, some registries
include
* IANA, which hands out OIDs under the "Private Enterprises"
branch,
* ANSI, which hands out OIDs under the "US Organizations" branch,
and
* BSI, which hands out OIDs under the "UK Organizations" branch.
o URN namespaces - IANA registers URN Namespace IDs (NIDs
[RFC8141]), and the organization registering an NID is responsible
for allocations of URNs within that namespace.
4.4. First Come First Served
For the First Come First Served policy, assignments are made to
anyone on a first come, first served basis. There is no substantive
review of the request, other than to ensure that it is well-formed
and doesn't duplicate an existing assignment. However, requests must
include a minimal amount of clerical information, such as a point of
contact (including an email address, and sometimes a postal address)
and a brief description of how the value will be used. Additional
information specific to the type of value requested may also need to
be provided, as defined by the namespace. For numbers, IANA
generally assigns the next in-sequence unallocated value, but other
values may be requested and assigned if an extenuating circumstance
exists. With names, specific text strings can usually be requested.
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When creating a new registry with First Come First Served as the
registration policy, in addition to the contact person field or
reference, the registry should contain a field for change controller.
Having a change controller for each entry for these types of
registrations makes authorization of future modifications more clear.
See Section 2.3.
It is important that changes to the registration of a First Come
First Served code point retain compatibility with the current usage
of that code point, so changes need to be made with care. The change
controller should not, in most cases, be requesting incompatible
changes nor repurposing a registered code point. See also Sections
9.4 and 9.5.
A working group or any other entity that is developing a protocol
based on a First Come First Served code point has to be extremely
careful that the protocol retains wire compatibility with current use
of the code point. Once that is no longer true, the new work needs
to change to a different code point (and register that use at the
appropriate time).
It is also important to understand that First Come First Served
really has no filtering. Essentially, any well-formed request is
accepted.
Examples:
SASL mechanism names [RFC4422]
LDAP Protocol Mechanisms and LDAP Syntax [RFC4520]
4.5. Expert Review
For the Expert Review policy, review and approval by a designated
expert (see Section 5) is required. While this does not necessarily
require formal documentation, information needs to be provided with
the request for the designated expert to evaluate. The registry's
definition needs to make clear to registrants what information is
necessary. The actual process for requesting registrations is
administered by IANA (see Section 1.2 for details).
(This policy was also called "Designated Expert" in earlier editions
of this document. The current term is "Expert Review".)
The required documentation and review criteria, giving clear guidance
to the designated expert, should be provided when defining the
registry. It is particularly important to lay out what should be
considered when performing an evaluation and reasons for rejecting a
request. It is also a good idea to include, when possible, a sense
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of whether many registrations are expected over time, or if the
registry is expected to be updated infrequently or in exceptional
circumstances only.
Thorough understanding of Section 5 is important when deciding on an
Expert Review policy and designing the guidance to the designated
expert.
Good examples of guidance to designated experts:
Extensible Authentication Protocol (EAP) [RFC3748], Sections 6 and
7.2
North-Bound Distribution of Link-State and TE Information Using
BGP [RFC7752], Section 5.1
When creating a new registry with Expert Review as the registration
policy, in addition to the contact person field or reference, the
registry should contain a field for change controller. Having a
change controller for each entry for these types of registrations
makes authorization of future modifications more clear. See
Section 2.3.
Examples:
EAP Method Types [RFC3748]
HTTP Digest AKA algorithm versions [RFC4169]
URI schemes [RFC7595]
GEOPRIV Location Types [RFC4589]
4.6. Specification Required
For the Specification Required policy, review and approval by a
designated expert (see Section 5) is required, and the values and
their meanings must be documented in a permanent and readily
available public specification, in sufficient detail so that
interoperability between independent implementations is possible.
This policy is the same as Expert Review, with the additional
requirement of a formal public specification. In addition to the
normal review of such a request, the designated expert will review
the public specification and evaluate whether it is sufficiently
stable and permanent, and sufficiently clear and technically sound to
allow interoperable implementations.
The intention behind "permanent and readily available" is that a
document can reasonably be expected to be findable and retrievable
long after IANA assignment of the requested value. Publication of an
RFC is an ideal means of achieving this requirement, but
Specification Required is intended to also cover the case of a
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document published outside of the RFC path, including informal
documentation.
For RFC publication, formal review by the designated expert is still
requested, but the normal RFC review process is expected to provide
the necessary review for interoperability. The designated expert's
review is still important, but it's equally important to note that
when there is IETF consensus, the expert can sometimes be "in the
rough" (see also the last paragraph of Section 5.4).
As with Expert Review (Section 4.5), clear guidance to the designated
expert should be provided when defining the registry, and thorough
understanding of Section 5 is important.
When specifying this policy, just use the term "Specification
Required". Some specifications have chosen to refer to it as "Expert
Review with Specification Required", and that only causes confusion.
Examples:
Diffserv-aware TE Bandwidth Constraints Model Identifiers
[RFC4124]
TLS ClientCertificateType Identifiers 64-223 [RFC5246]
ROHC Profile Identifiers [RFC5795]
4.7. RFC Required
With the RFC Required policy, the registration request, along with
associated documentation, must be published in an RFC. The RFC need
not be in the IETF stream, but may be in any RFC stream (currently an
RFC may be in the IETF, IRTF, IAB, or Independent Submission streams
[RFC5742]).
Unless otherwise specified, any type of RFC is sufficient (currently
Standards Track, BCP, Informational, Experimental, or Historic).
Examples:
DNSSEC DNS Security Algorithm Numbers [RFC6014]
Media Control Channel Framework registries [RFC6230]
DANE TLSA Certificate Usages [RFC6698]
4.8. IETF Review
(Formerly called "IETF Consensus" in the first edition of this
document.) With the IETF Review policy, new values are assigned only
through RFCs in the IETF Stream -- those that have been shepherded
through the IESG as AD-Sponsored or IETF working group documents
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[RFC2026] [RFC5378], have gone through IETF Last Call, and have been
approved by the IESG as having IETF consensus.
The intent is that the document and proposed assignment will be
reviewed by the IETF community (including appropriate IETF working
groups, directorates, and other experts) and by the IESG, to ensure
that the proposed assignment will not negatively affect
interoperability or otherwise extend IETF protocols in an
inappropriate or damaging manner.
Unless otherwise specified, any type of RFC is sufficient (currently
Standards Track, BCP, Informational, Experimental, or Historic).
Examples:
IPSECKEY Algorithm Types [RFC4025]
TLS Extension Types [RFC5246]
4.9. Standards Action
For the Standards Action policy, values are assigned only through
Standards Track or Best Current Practice RFCs in the IETF Stream.
Examples:
BGP message types [RFC4271]
Mobile Node Identifier option types [RFC4283]
TLS ClientCertificateType Identifiers 0-63 [RFC5246]
DCCP Packet Types [RFC4340]
4.10. IESG Approval
New assignments may be approved by the IESG. Although there is no
requirement that the request be documented in an RFC, the IESG has
the discretion to request documents or other supporting materials on
a case-by-case basis.
IESG Approval is not intended to be used often or as a "common case";
indeed, it has seldom been used in practice. Rather, it is intended
to be available in conjunction with other policies as a fall-back
mechanism in the case where one of the other allowable approval
mechanisms cannot be employed in a timely fashion or for some other
compelling reason. IESG Approval is not intended to circumvent the
public review processes implied by other policies that could have
been employed for a particular assignment. IESG Approval would be
appropriate, however, in cases where expediency is desired and there
is strong consensus (such as from a working group) for making the
assignment.
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Before approving a request, the IESG might consider consulting the
community, via a "call for comments" that provides as much
information as is reasonably possible about the request.
Examples:
IPv4 Multicast address assignments [RFC5771]
IPv4 IGMP Type and Code values [RFC3228]
Mobile IPv6 Mobility Header Type and Option values [RFC6275]
4.11. Using the Well-Known Registration Policies
Because the well-known policies benefit from both community
experience and wide understanding, their use is encouraged, and the
creation of new policies needs to be accompanied by reasonable
justification.
It is also acceptable to cite one or more well-known policies and
include additional guidelines for what kind of considerations should
be taken into account by the review process.
For example, for media-type registrations [RFC6838], a number of
different situations are covered that involve the use of IETF Review
and Specification Required, while also including specific additional
criteria the designated expert should follow. This is not meant to
represent a registration procedure, but to show an example of what
can be done when special circumstances need to be covered.
The well-known policies from "First Come First Served" to "Standards
Action" specify a range of policies in increasing order of strictness
(using the numbering from the full list in Section 4):
4. First Come First Served
No review, minimal documentation.
5 and 6 (of equal strictness).
5. Expert Review
Expert review with sufficient documentation for review.
6. Specification Required
Significant stable public documentation sufficient for
interoperability.
7. RFC Required
Any RFC publication, IETF or a non-IETF Stream.
8. IETF Review
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RFC publication, IETF Stream only, but need not be Standards
Track.
9. Standards Action
RFC publication, IETF Stream, Standards Track or BCP only.
Examples of situations that might merit IETF Review or Standards
Action include the following:
o When a resource is limited, such as bits in a byte (or in two
bytes, or four), or numbers in a limited range. In these cases,
allowing registrations that haven't been carefully reviewed and
agreed to by community consensus could too quickly deplete the
allowable values.
o When thorough community review is necessary to avoid extending or
modifying the protocol in ways that could be damaging. One
example is in defining new command codes, as opposed to options
that use existing command codes: the former might require a strict
policy, where a more relaxed policy could be adequate for the
latter. Another example is in defining protocol elements that
change the semantics of existing operations.
o When there are security implications with respect to the resource,
and thorough review is needed to ensure that the new usage is
sound. Examples of this include lists of acceptable hashing and
cryptographic algorithms, and assignment of transport ports in the
system range.
When reviewing a document that asks IANA to create a new registry or
change a registration policy to any policy more stringent than Expert
Review or Specification Required, the IESG should ask for
justification to ensure that more relaxed policies have been
considered and that the more strict policy is the right one.
Accordingly, document developers need to anticipate this and document
their considerations for selecting the specified policy (ideally, in
the document itself; failing that, in the shepherd writeup).
Likewise, the document shepherd should ensure that the selected
policies have been justified before sending the document to the IESG.
When specifications are revised, registration policies should be
reviewed in light of experience since the policies were set.
4.12. Using Multiple Policies in Combination
In some situations, it is necessary to define multiple registration
policies. For example, registrations through the normal IETF process
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might use one policy, while registrations from outside the process
would have a different policy applied.
Thus, a particular registry might want to use a policy such as "RFC
Required" or "IETF Review" sometimes, with a designated expert
checking a "Specification Required" policy at other times.
The alternative to using a combination requires either that all
requests come through RFCs or that requests in RFCs go through review
by the designated expert, even though they already have IETF review
and consensus.
This can be documented in the IANA Considerations section when the
registry is created, for example:
IANA is asked to create the registry "Fruit Access Flags" under
the "Fruit Parameters" group. New registrations will be permitted
through either the IETF Review policy or the Specification
Required policy [BCP26]. The latter should be used only for
registrations requested by SDOs outside the IETF. Registrations
requested in IETF documents will be subject to IETF review.
Such combinations will commonly use one of {Standards Action, IETF
Review, RFC Required} in combination with one of {Specification
Required, Expert Review}. Guidance should be provided about when
each policy is appropriate, as in the example above.
4.13. Provisional Registrations
Some existing registries have policies that allow provisional
registration: see URI Schemes [RFC7595] and Email Header Fields
[RFC3864]. Registrations that are designated as provisional are
usually defined as being more readily created, changed, reassigned,
moved to another status, or removed entirely. URI Schemes, for
example, allow provisional registrations to be made with incomplete
information.
Allowing provisional registration ensures that the primary goal of
maintaining a registry -- avoiding collisions between incompatible
semantics -- is achieved without the side effect of "endorsing" the
protocol mechanism the provisional value is used for. Provisional
registrations for codepoints that are ultimately standardized can be
promoted to permanent status. The criteria that are defined for
converting a provisional registration to permanent will likely be
more strict than those that allowed the provisional registration.
If your registry does not have a practical limit on codepoints,
perhaps adding the option for provisional registrations might be
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right for that registry as well.
5. Designated Experts5.1. The Motivation for Designated Experts
Discussion on a mailing list can provide valuable technical feedback,
but opinions often vary and discussions may continue for some time
without clear resolution. In addition, IANA cannot participate in
all of these mailing lists and cannot determine if or when such
discussions reach consensus. Therefore, IANA relies on a "designated
expert" for advice regarding the specific question of whether an
assignment should be made. The designated expert is an individual
who is responsible for carrying out an appropriate evaluation and
returning a recommendation to IANA.
It should be noted that a key motivation for having designated
experts is for the IETF to provide IANA with a subject matter expert
to whom the evaluation process can be delegated. IANA forwards
requests for an assignment to the expert for evaluation, and the
expert (after performing the evaluation) informs IANA as to whether
or not to make the assignment or registration. In most cases, the
registrants do not work directly with the designated experts. The
list of designated experts for a registry is listed in the registry.
It will often be useful to use a designated expert only some of the
time, as a supplement to other processes. For more discussion of
that topic, see Section 4.12.
5.2. The Role of the Designated Expert
The designated expert is responsible for coordinating the appropriate
review of an assignment request. The review may be wide or narrow,
depending on the situation and the judgment of the designated expert.
This may involve consultation with a set of technology experts,
discussion on a public mailing list, consultation with a working
group (or its mailing list if the working group has disbanded), etc.
Ideally, the designated expert follows specific review criteria as
documented with the protocol that creates or uses the namespace. See
the IANA Considerations sections of [RFC3748] and [RFC3575] for
specific examples.
Designated experts are expected to be able to defend their decisions
to the IETF community, and the evaluation process is not intended to
be secretive or bestow unquestioned power on the expert. Experts are
expected to apply applicable documented review or vetting procedures,
or in the absence of documented criteria, follow generally accepted
norms such as those in Section 5.3. Designated experts are generally
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not expected to be "gatekeepers", setting out to make registrations
difficult to obtain, unless the guidance in the defining document
specifies that they should act as such. Absent stronger guidance,
the experts should be evaluating registration requests for
completeness, interoperability, and conflicts with existing protocols
and options.
It has proven useful to have multiple designated experts for some
registries. Sometimes those experts work together in evaluating a
request, while in other cases additional experts serve as backups,
acting only when the primary expert is unavailable. In registries
with a pool of experts, the pool often has a single chair responsible
for defining how requests are to be assigned to and reviewed by
experts. In other cases, IANA might assign requests to individual
members in sequential or approximate random order. The document
defining the registry can, if it's appropriate for the situation,
specify how the group should work -- for example, it might be
appropriate to specify rough consensus on a mailing list, within a
related working group or among a pool of designated experts.
In cases of disagreement among multiple experts, it is the
responsibility of those experts to make a single clear recommendation
to IANA. It is not appropriate for IANA to resolve disputes among
experts. In extreme situations, such as deadlock, the designating
body may need to step in to resolve the problem.
If a designated expert has a conflict of interest for a particular
review (is, for example, an author or significant proponent of a
specification related to the registration under review), that expert
should recuse himself. In the event that all the designated experts
are conflicted, they should ask that a temporary expert be designated
for the conflicted review. The responsible AD may then appoint
someone or the AD may handle the review.
This document defines the designated expert mechanism with respect to
documents in the IETF stream only. If other streams want to use
registration policies that require designated experts, it is up to
those streams (or those documents) to specify how those designated
experts are appointed and managed. What is described below, with
management by the IESG, is only appropriate for the IETF stream.
5.2.1. Managing Designated Experts in the IETF
Designated experts for registries created by the IETF are appointed
by the IESG, normally upon recommendation by the relevant Area
Director. They may be appointed at the time a document creating or
updating a namespace is approved by the IESG, or subsequently, when
the first registration request is received. Because experts
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originally appointed may later become unavailable, the IESG will
appoint replacements as necessary. The IESG may remove any
designated expert that it appointed, at its discretion.
The normal appeals process, as described in [RFC2026], Section 6.5.1,
applies to issues that arise with the designated expert team. For
this purpose, the designated expert team takes the place of the
working group in that description.
5.3. Designated Expert Reviews
In the years since [RFC2434] was published and put to use, experience
has led to the following observations:
o A designated expert must respond in a timely fashion, normally
within a week for simple requests to a few weeks for more complex
ones. Unreasonable delays can cause significant problems for
those needing assignments, such as when products need code points
to ship. This is not to say that all reviews can be completed
under a firm deadline, but they must be started, and the requester
and IANA should have some transparency into the process if an
answer cannot be given quickly.
o If a designated expert does not respond to IANA's requests within
a reasonable period of time, either with a response or with a
reasonable explanation for the delay (some requests may be
particularly complex), and if this is a recurring event, IANA must
raise the issue with the IESG. Because of the problems caused by
delayed evaluations and assignments, the IESG should take
appropriate actions to ensure that the expert understands and
accepts his or her responsibilities, or appoint a new expert.
o The designated expert is not required to personally bear the
burden of evaluating and deciding all requests, but acts as a
shepherd for the request, enlisting the help of others as
appropriate. In the case that a request is denied, and rejecting
the request is likely to be controversial, the expert should have
the support of other subject matter experts. That is, the expert
must be able to defend a decision to the community as a whole.
When a designated expert is used, the documentation should give clear
guidance to the designated expert, laying out criteria for performing
an evaluation and reasons for rejecting a request. In the case where
there are no specific documented criteria, the presumption should be
that a code point should be granted unless there is a compelling
reason to the contrary (and see also Section 5.4). Reasons that have
been used to deny requests have included these:
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o Scarcity of code points, where the finite remaining code points
should be prudently managed, or where a request for a large number
of code points is made and a single code point is the norm.
o Documentation is not of sufficient clarity to evaluate or ensure
interoperability.
o The code point is needed for a protocol extension, but the
extension is not consistent with the documented (or generally
understood) architecture of the base protocol being extended and
would be harmful to the protocol if widely deployed. It is not
the intent that "inconsistencies" refer to minor differences "of a
personal preference nature". Instead, they refer to significant
differences such as inconsistencies with the underlying security
model, implying a change to the semantics of an existing message
type or operation, requiring unwarranted changes in deployed
systems (compared with alternate ways of achieving a similar
result), etc.
o The extension would cause problems with existing deployed systems.
o The extension would conflict with one under active development by
the IETF, and having both would harm rather than foster
interoperability.
Documents must not name the designated expert(s) in the document
itself; instead, any suggested names should be relayed to the
appropriate Area Director at the time the document is sent to the
IESG for approval. This is usually done in the document shepherd
writeup.
If the request should also be reviewed on a specific public mailing
list, its address should be specified.
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Review by the designated expert is necessarily done at a particular
point in time and represents review of a particular version of the
document. While reviews are generally done around the time of IETF
Last Call, deciding when the review should take place is a question
of good judgment. And while rereviews might be done when it's
acknowledged that the documentation of the registered item has
changed substantially, making sure that rereview happens requires
attention and care.
It is possible, through carelessness, accident, inattentiveness, or
even willful disregard, that changes might be made after the
designated expert's review and approval that would, if the document
were rereviewed, cause the expert not to approve the registration.
It is up to the IESG, with the token held by the responsible Area
Director, to be alert to such situations and to recognize that such
changes need to be checked.
For registrations made from documents on the Standards Track, there
is often expert review required (by the registration policy) in
addition to IETF consensus (for approval as a Standards Track RFC).
In such cases, the review by the designated expert needs to be
timely, submitted before the IESG evaluates the document. The IESG
should generally not hold the document up waiting for a late review.
It is also not intended for the expert review to override IETF
consensus: the IESG should consider the review in its own evaluation,
as it would do for other Last Call reviews.
6. Well-Known Registration Status Terminology
The following labels describe the status of an assignment or range of
assignments:
Private Use: Private use only (not assigned), as described in
Section 4.1.
Experimental: Available for general experimental use as described
in [RFC3692]. IANA does not record specific assignments for
any particular use.
Unassigned: Not currently assigned, and available for assignment
via documented procedures. While it's generally clear that
any values that are not registered are unassigned and
available for assignment, it is sometimes useful to
explicitly specify that situation. Note that this is
distinctly different from "Reserved".
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Reserved: Not assigned and not available for assignment.
Reserved values are held for special uses, such as to extend
the namespace when it becomes exhausted. "Reserved" is also
sometimes used to designate values that had been assigned
but are no longer in use, keeping them set aside as long as
other unassigned values are available. Note that this is
distinctly different from "Unassigned".
Reserved values can be released for assignment by the change
controller for the registry (this is often the IESG, for
registries created by RFCs in the IETF stream).
Known Unregistered Use: It's known that the assignment or range
is in use without having been defined in accordance with
reasonable practice. Documentation for use of the
assignment or range may be unavailable, inadequate, or
conflicting. This is a warning against use, as well as an
alert to network operators who might see these values in use
on their networks.
7. Documentation References in IANA Registries
Usually, registries and registry entries include references to
documentation (RFCs or other documents). The purpose of these
references is to provide pointers for implementors to find details
necessary for implementation, NOT to simply note what document
created the registry or entry. Therefore:
o If a document registers an item that is defined and explained
elsewhere, the registered reference should be to the document
containing the definition, not to the document that is merely
performing the registration.
o If the registered item is defined and explained in the current
document, it is important to include sufficient information to
enable implementors to understand the item and to create a proper
implementation.
o If the registered item is explained primarily in a specific
section of the reference document, it is useful to include a
section reference. For example, "[RFC4637], Section 3.2", rather
than just "[RFC4637]".
o For documentation of a new registry, the reference should provide
information about the registry itself, not just a pointer to the
creation of it. Useful information includes the purpose of the
registry, a rationale for its creation, documentation of the
process and policy for new registrations, guidelines for new
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registrants or designated experts, and other such related
information. But note that, while it's important to include this
information in the document, it needn't all be in the IANA
Considerations section. See Section 1.1.
8. What to Do in "bis" Documents
On occasion, an RFC is issued that obsoletes a previous edition of
the same document. We sometimes call these "bis" documents, such as
when RFC 4637 is to be obsoleted by draft-ietf-foo-rfc4637bis. When
the original document created registries and/or registered entries,
there is a question of how to handle the IANA Considerations section
in the "bis" document.
If the registrations specify the original document as a reference,
those registrations should be updated to point to the current (not
obsolete) documentation for those items. Usually, that will mean
changing the reference to be the "bis" document.
There will, though, be times when a document updates another, but
does not make it obsolete, and the definitive reference is changed
for some items but not for others. Be sure that the references
always point to the correct, current documentation for each item.
For example, suppose RFC 4637 registered the "BANANA" flag in the
"Fruit Access Flags" registry, and the documentation for that flag is
in Section 3.2.
The current registry might look, in part, like this:
Name Description Reference
-------- ------------------- ---------
BANANA Flag for bananas [RFC4637], Section 3.2
If draft-ietf-foo-rfc4637bis obsoletes RFC 4637 and, because of some
rearrangement, now documents the flag in Section 4.1.2, the IANA
Considerations of the bis document might contain text such as this:
IANA is asked to change the registration information for the
BANANA flag in the "Fruit Access Flags" registry to the
following:
Name Description Reference
-------- ------------------- ---------
BANANA Flag for bananas [[this RFC]], Section 4.2.1Cotton, et al. Best Current Practice [Page 33]

RFC 8126 IANA Considerations Section in RFCs June 2017
In many cases, if there are a number of registered references to the
original RFC and the document organization has not changed the
registered section numbering much, it may simply be reasonable to do
this:
Because this document obsoletes RFC 4637, IANA is asked to change
all registration information that references [RFC4637] to instead
reference [[this RFC]].
If information for registered items has been or is being moved to
other documents, then the registration information should be changed
to point to those other documents. In most cases, documentation
references should not be left pointing to the obsoleted document for
registries or registered items that are still in current use. For
registries or registered items that are no longer in current use, it
will usually make sense to leave the references pointing to the old
document -- the last current reference for the obsolete items. The
main point is to make sure that the reference pointers are as useful
and current as is reasonable, and authors should consider that as
they write the IANA Considerations for the new document. As always:
do the right thing, and there is flexibility to allow for that.
It is extremely important to be clear in your instructions regarding
updating references, especially in cases where some references need
to be updated and others do not.
9. Miscellaneous Issues9.1. When There Are No IANA Actions
Before an Internet-Draft can be published as an RFC, IANA needs to
know what actions (if any) it needs to perform. Experience has shown
that it is not always immediately obvious whether a document has no
IANA actions, without reviewing the document in some detail. In
order to make it clear to IANA that it has no actions to perform (and
that the author has consciously made such a determination), such
documents should, after the authors confirm that this is the case,
include an IANA Considerations section that states:
This document has no IANA actions.
IANA prefers that these "empty" IANA Considerations sections be left
in the document for the record: it makes it clear later on that the
document explicitly said that no IANA actions were needed (and that
it wasn't just omitted). This is a change from the prior practice of
requesting that such sections be removed by the RFC Editor, and
authors are asked to accommodate this change.
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RFC 8126 IANA Considerations Section in RFCs June 20179.2. Namespaces Lacking Documented Guidance
For all existing RFCs that either explicitly or implicitly rely on
IANA to make assignments without specifying a precise assignment
policy, IANA will work with the IESG to decide what policy is
appropriate. Changes to existing policies can always be initiated
through the normal IETF consensus process, or through the IESG when
appropriate.
All future RFCs that either explicitly or implicitly rely on IANA to
register or otherwise administer namespace assignments must provide
guidelines for administration of the namespace.
9.3. After-the-Fact Registrations
Occasionally, the IETF becomes aware that an unassigned value from a
namespace is in use on the Internet or that an assigned value is
being used for a different purpose than it was registered for. The
IETF does not condone such misuse; procedures of the type described
in this document need to be applied to such cases, and it might not
always be possible to formally assign the desired value. In the
absence of specifications to the contrary, values may only be
reassigned for a different purpose with the consent of the original
assignee (when possible) and with due consideration of the impact of
such a reassignment. In cases of likely controversy, consultation
with the IESG is advised.
This is part of the reason for the advice in Section 3.1 about using
placeholder values, such as "TBD1", during document development:
problems are often caused by the open use of unregistered values
after results from well-meant, early implementations, where the
implementations retained the use of developmental code points that
never proceeded to a final IANA assignment.
9.4. Reclaiming Assigned Values
Reclaiming previously assigned values for reuse is tricky, because
doing so can lead to interoperability problems with deployed systems
still using the assigned values. Moreover, it can be extremely
difficult to determine the extent of deployment of systems making use
of a particular value. However, in cases where the namespace is
running out of unassigned values and additional ones are needed, it
may be desirable to attempt to reclaim unused values. When
reclaiming unused values, the following (at a minimum) should be
considered:
Cotton, et al. Best Current Practice [Page 35]

RFC 8126 IANA Considerations Section in RFCs June 2017
o Attempts should be made to contact the original party to which a
value is assigned, to determine if the value was ever used, and if
so, the extent of deployment. (In some cases, products were never
shipped or have long ceased being used. In other cases, it may be
known that a value was never actually used at all.)
o Reassignments should not normally be made without the concurrence
of the original requester. Reclamation under such conditions
should only take place where there is strong evidence that a value
is not widely used, and the need to reclaim the value outweighs
the cost of a hostile reclamation. IESG Approval is needed in
this case.
o It may be appropriate to write up the proposed action and solicit
comments from relevant user communities. In some cases, it may be
appropriate to write an RFC that goes through a formal IETF
process (including IETF Last Call) as was done when DHCP reclaimed
some of its "Private Use" options [RFC3942].
o It may be useful to differentiate between revocation, release, and
transfer. Revocation occurs when IANA removes an assignment,
release occurs when the assignee initiates that removal, and
transfer occurs when either revocation or release is coupled with
immediate reassignment. It may be useful to specify procedures
for each of these or to explicitly prohibit combinations that are
not desired.
9.5. Contact Person vs Assignee or Owner
Many registries include designation of a technical or administrative
contact associated with each entry. Often, this is recorded as
contact information for an individual. It is unclear, though, what
role the individual has with respect to the registration: is this
item registered on behalf of the individual, the company the
individual worked for, or perhaps another organization the individual
was acting for?
This matters because some time later, when the individual has changed
jobs or roles, and perhaps can no longer be contacted, someone might
want to update the registration. IANA has no way to know what
company, organization, or individual should be allowed to take the
registration over. For registrations rooted in RFCs, the stream
owner (such as the IESG or the IAB) can make an overriding decision.
But in other cases, there is no recourse.
Registries can include, in addition to a "Contact" field, an
"Assignee" or "Owner" field (also referred to as "Change Controller")
that can be used to address this situation, giving IANA clear
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RFC 8126 IANA Considerations Section in RFCs June 2017
guidance as to the actual owner of the registration. This is
strongly advised, especially for registries that do not require RFCs
to manage their information (e.g., registries with policies such as
First Come First Served (Section 4.4), Expert Review (Section 4.5),
and Specification Required (Section 4.6)). Alternatively,
organizations can put an organizational role into the "Contact" field
in order to make their ownership clear.
9.6. Closing or Obsoleting a Registry/Registrations
Sometimes there is a request to "close" a registry to further
registrations. When a registry is closed, no further registrations
will be accepted. The information in the registry will still be
valid and registrations already in the registry can still be updated.
A closed registry can also be marked as "obsolete", as an indication
that the information in the registry is no longer in current use.
Specific entries in a registry can be marked as "obsolete" (no longer
in use) or "deprecated" (use is not recommended).
Such changes to registries and registered values are subject to
normal change controls (see Section 2.3). Any closure, obsolescence,
or deprecation serves to annotate the registry involved; the
information in the registry remains there for informational and
historic purposes.
10. Appeals
Appeals of protocol parameter registration decisions can be made
using the normal IETF appeals process as described in [RFC2026],
Section 6.5. That is, an initial appeal should be directed to the
IESG, followed (if necessary) by an appeal to the IAB.
11. Mailing Lists
All IETF mailing lists associated with evaluating or discussing
assignment requests as described in this document are subject to
whatever rules of conduct and methods of list management are
currently defined by best current practices or by IESG decision.
12. Security Considerations
Information that creates or updates a registration needs to be
authenticated and authorized. IANA updates registries according to
instructions in published RFCs and from the IESG. It may also accept
clarifications from document authors, relevant working group chairs,
designated experts, and mail list participants.
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RFC 8126 IANA Considerations Section in RFCs June 2017
Information concerning possible security vulnerabilities of a
protocol may change over time. Likewise, security vulnerabilities
related to how an assigned number is used may change as well. As new
vulnerabilities are discovered, information about such
vulnerabilities may need to be attached to existing registrations so
that users are not misled as to the true security issues surrounding
the use of a registered number.
Security needs to be considered as part of the selection of a
registration policy. For some protocols, registration of certain
parameters will have security implications, and registration policies
for the relevant registries must ensure that requests get appropriate
review with those security implications in mind.
An analysis of security issues is generally required for all
protocols that make use of parameters (data types, operation codes,
keywords, etc.) documented in IETF protocols or registered by IANA.
Such security considerations are usually included in the protocol
document [BCP72]. It is the responsibility of the IANA
considerations associated with a particular registry to specify
whether value-specific security considerations must be provided when
assigning new values and the process for reviewing such claims.
13. IANA Considerations
Sitewide, IANA has replaced references to RFC 5226 with references to
this document.
14. Changes Relative to Earlier Editions of BCP 2614.1. 2016: Changes in This Document Relative to RFC 5226
Significant additions:
o Removed RFC 2119 key words, boilerplate, and reference, preferring
plain English -- this is not a protocol specification.
o Added Section 1.1, Keep IANA Considerations for IANA
o Added Section 1.2, For Updated Information
o Added Section 2.1, Organization of Registries
o Added best practice for selecting an appropriate policy into
Section 4.
o Added Section 4.12, Using Multiple Policies in Combination
Cotton, et al. Best Current Practice [Page 38]

RFC 8126 IANA Considerations Section in RFCs June 2017
o Added Section 2.3, Specifying Change Control for a Registry
o Added Section 3.4, Early Allocations
o Moved each well-known policy into a separate subsection of
Section 4.
o Added Section 5.4, Expert Reviews and the Document Lifecycle
o Added Section 7, Documentation References in IANA Registries
o Added Section 8, What to Do in "bis" Documents
o Added Section 9.5, Contact Person vs Assignee or Owner
o Added Section 9.6, Closing or Obsoleting a Registry/Registrations
Clarifications and such:
o Some reorganization -- moved text around for clarity and easier
reading.
o Made clarifications about identification of IANA registries and
use of URLs for them.
o Clarified the distinction between "Unassigned" and "Reserved".
o Made some clarifications in "Expert Review" about instructions to
the designated expert.
o Made some clarifications in "Specification Required" about how to
declare this policy.
o Assorted minor clarifications and editorial changes throughout.
14.2. 2008: Changes in RFC 5226 Relative to RFC 2434
Changes include:
o Major reordering of text to expand descriptions and to better
group topics such as "updating registries" vs. "creating new
registries", in order to make it easier for authors to find the
text most applicable to their needs.
o Numerous editorial changes to improve readability.
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RFC 8126 IANA Considerations Section in RFCs June 2017
o Changed the term "IETF Consensus" to "IETF Review" and added more
clarifications. History has shown that people see the words "IETF
Consensus" (without consulting the actual definition) and are
quick to make incorrect assumptions about what the term means in
the context of IANA Considerations.
o Added "RFC Required" to list of defined policies.
o Much more explicit directions and examples of "what to put in
RFCs".
o "Specification Required" now implies use of a designated expert to
evaluate specs for sufficient clarity.
o Added a section describing provisional registrations.
o Significantly changed the wording in the "Designated Experts"
section. Main purpose is to make clear that Expert Reviewers are
accountable to the community, and to provide some guidance for
review criteria in the default case.
o Changed wording to remove any special appeals path. The normal
RFC 2026 appeals path is used.
o Added a section about reclaiming unused values.
o Added a section on after-the-fact registrations.
o Added a section indicating that mailing lists used to evaluate
possible assignments (such as by a designated expert) are subject
to normal IETF rules.
15. References15.1. Normative References
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, DOI 10.17487/RFC2026, October 1996,
<http://www.rfc-editor.org/info/rfc2026>.
15.2. Informative References
[BCP72] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552, July
2003, <http://www.rfc-editor.org/info/bcp72>.
Cotton, et al. Best Current Practice [Page 40]

RFC 8126 IANA Considerations Section in RFCs June 2017
Acknowledgments for This Document (2017)
Thomas Narten and Harald Tveit Alvestrand edited the two earlier
editions of this document (RFCs 2434 and 5226), and Thomas continues
his role in this third edition. Much of the text from RFC 5226
remains in this edition.
Thank you to Amanda Baber and Pearl Liang for their multiple reviews
and suggestions for making this document as thorough as possible.
This document has benefited from thorough review and comments by many
people, including Benoit Claise, Alissa Cooper, Adrian Farrel,
Stephen Farrell, Tony Hansen, John Klensin, Kathleen Moriarty, Mark
Nottingham, Pete Resnick, and Joe Touch.
Special thanks to Mark Nottingham for reorganizing some of the text
for better organization and readability, to Tony Hansen for acting as
document shepherd, and to Brian Haberman and Terry Manderson for
acting as sponsoring ADs.
Acknowledgments from the Second Edition (2008)
The original acknowledgments section in RFC 5226 was:
This document has benefited from specific feedback from Jari Arkko,
Marcelo Bagnulo Braun, Brian Carpenter, Michelle Cotton, Spencer
Dawkins, Barbara Denny, Miguel Garcia, Paul Hoffman, Russ Housley,
John Klensin, Allison Mankin, Blake Ramsdell, Mark Townsley, Magnus
Westerlund, and Bert Wijnen.
Acknowledgments from the First Edition (1998)
The original acknowledgments section in RFC 2434 was:
Jon Postel and Joyce Reynolds provided a detailed explanation on what
IANA needs in order to manage assignments efficiently, and patiently
provided comments on multiple versions of this document. Brian
Carpenter provided helpful comments on earlier versions of the
document. One paragraph in the Security Considerations section was
borrowed from RFC 4288.
Cotton, et al. Best Current Practice [Page 46]